Self-centering device for linear drive units

ABSTRACT

A linear unit ( 1 ) comprising a profiled rail ( 2 ) along which a carriage ( 3 ) is arranged for sliding motion backwards and forwards by means of a reversible screw ( 4 ) which actuates the carriage and on either side of the carriage passes through a bore ( 7 ) in a screw support ( 8 ). A pull rod ( 24 ) displaces the screw support backwards and forwards along the profiled rail between to end stop positions, and the screw support serves as a support bearing carrying the screw between bearings ( 10 ) supporting the screw at its ends. A self-centering device for automatic centering of the screw in the screw support is formed with a self-centering element ( 11 ) mounted in the screw-support bore, said element slidingly abutting against the screw both when the screw is rotating in either one of its directions of rotation and when the screw support assumes its end stop positions. The pull rod kinetically interconnects the screw supports located on either side of the carriage, whereby as the carriage is displaced in a sliding motion in one direction it will abut against the screw support located on one side of the carriage for displacement of said screw support from one of its end stop positions to the other one while simultaneously, via the pull rod, bringing along in its movement the screw support located on the other side of the carriage, and reversely.

TECHNICAL FIELD OF INVENTION

The present invention relates to a device for linear drive units of thetype comprising a profiled rail along which a carriage is arranged forsliding movement backwards and forwards in response to actuation from athreaded screw, said screw arranged to rotate in two opposite directionsand being drivingly connected with the carriage and, on either side ofthe carriage, passing freely through a through-bore in at least onescrew support, said support being arranged to be displaced by means of adriver means for movement backwards and forwards along the profiled railbetween two end stop positions and forming bearing means carrying saidscrew intermediate end bearings that support the screw at the ends ofthe latter.

BACKGROUND OF THE INVENTION

Screw supports of this kind primarily serve to counteract tendencies ofthe screw, which usually is a ball screw, to start vibrating and bendingor being deflected outwards, when the screw reaches a criticalrotational speed. Such lateral deflections depend among other things onthe length of the screw and its rotational speed. When the screw is longand/or rotates at a high speed, this critical rotational-speed value isreached at an earlier stage than when the screw is shorter and/orrotates at a lower speed.

In the case of long linear units having a length of several meters, upto six meters, and being fitted with a long screw of a correspondinglength, such tendencies to deflection outwards of the screw may becounteracted with the aid of two or more such screw supports. To allowthe carriage to be slid from one end of the linear unit to the oppositeone, various driver means have been suggested to displace the screwsupports from a first end stop position along the longitudinal extensionof the screw to another end stop position and then, in a returndisplacement movement, return the screw supports to their first end stopposition.

A prior-art driver means configured as interacting locking means betweencarriage and screw supports suffers from the disadvantage of beingunnecessarily complicated and in addition exposed to excess wear fromthe displacement of the screw supports backwards and forwards betweenthe end stop positions by means of the carriage, a feature which oftenleads to unsatisfactory operational reliability and stability of thelinear unit.

Often, such interacting locking means also require so much space in thearea around the linear unit that there is a risk that, while moving, thescrew supports hook onto some component of the linear unit, whichlikewise impairs the operational reliability and stability of the linearunit and may lead to breakdowns. In addition, interacting locking meansbetween carriage and screw supports of a kind that are constantlyinterconnected and disconnected mechanically generate a strongpercussion-like noise, which often is felt as most disturbing.

In another prior-art and much improved driver means that eliminatesentirely the need for interacting locking means acting between carriageand screw supports, the screw and the screw support are fitted withinteracting driver means which, upon rotation of the screw in onedirection, carry with them the screw support, displacing it from one ofits stop end position to the opposite one and reversely, and which meansslide on top of the screw in the end stop positions of the screw supportuntil the screw changes its direction of rotation.

Irrespective of the length of the linear unit and the type of the drivermeans therein, the screw ends are mounted to ensure that they arecentered in their associated bearings. Because of such factors asinevitable manufacturing and matching tolerances and wear on the onehand between screw and screw support and on the other between screwsupport and profiled rail, play and misalignment of the screw supportsrelative to the screw and the profiled rail often arise, particularlywhen the linear unit has been in use for some time. In turn, this leadsto the screw supports being exposed to uneven loads from the screwduring their movement backwards and forwards along the profiled rail,usually because the screw, when rotating, constantly or alternatelyexerts pressure on one or the other of the sides of the through-boreformed in the screw support, with consequential increase of wear andnoise and in the end functional disturbances and even breakdown.

OBJECT OF THE INVENTION

The principal object of the present invention is to eliminate thedisadvantages outlined above and to propose a device which,independently of tolerances, play and misalignment of the screw supportsrelative to the screw and the profiled rail, ensures that at all timesthe screw extends as straight as possible from one of its end bearingsto the opposite one without exerting uneven load on the screw supports.

Another object of the invention is to propose a device of the kinddefined above which efficiently counteracts and consequently reduces thetendency of the rotating screw to bend or be deflected outwards as itreaches a critical rotational speed.

Yet another object of the invention is to propose a device that isextremely simple and reliable as to its structure and function.

A further object of the invention is to propose a device possessingextremely high sliding and wear-resistance properties.

It is likewise an object of the invention to propose a device thatoperates extremely silently.

SUMMARY OF THE INVENTION

These and other objects of the invention are achieved in a manner thatis as ingenious as it is unique by means of a self-centering elementlocated in the through-bore of the screw support, which element hassliding contact with the screw both when the screw is rotating in one orthe other of its directions and when the screw supports assume their endstop positions, in order to self-center the screw in the screw support.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail in the following withreference to the accompanying drawings, wherein

FIG. 1 is a longitudinal sectional view through a linear unit inaccordance with a preferred embodiment of the invention comprising twoscrew supports;

FIG. 2 is a cross-sectional view through the linear unit, the sectionbeing taken along line II—II of FIG. 1;

FIG. 3 is a longitudinal sectional view through a part of the linearunit, the section being taken along line III—III of FIG. 2;

FIG. 4 is a cross-sectional view through one of the screw supports alongline IV—IV of FIG. 1, having a self-centering element in accordance witha first preferred embodiment.

FIG. 5 is a longitudinal sectional view along line V—V of FIG. 4.

FIG. 6 is a view as seen from the side and above and shows a plateincorporated in the self-centering element of the first preferredembodiment.

FIG. 7 is a cross-sectional view corresponding to FIG. 4 and shows asecond preferred embodiment of a self-centering element in the form of asleeve.

FIG. 8 is a cross-sectional view along line VIII—VIII of FIG. 7, and

FIGS. 9A, 9B, and 9C are views as seen from the side, from above andfrom the end, respectively, of a driver means in the form of a pull rodincorporated in the linear unit of FIGS. 1–3.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows in a longitudinal sectional view a linear unit, generallydesignated by numeral reference 1, said linear unit primarily intendedfor handling material within many diverse fields of industry where rapidand reliable handling of loads over large distances is required.

The principal components of the chosen linear unit 1 shown in thedrawing figures are a profiled rail 2, preferably an extrudedself-supporting aluminium profiled section, and a carriage 3, the latterbeing composed of a number of detail components preferably made fromaluminium and/or steel.

The carriage 3 is supported and guided in and on the profiled rail 2 insuch a manner as to be slidingly displaceable in a backwards andforwards movement in the longitudinal direction of the rail, as shown bythe double arrow A. In turn, the carriage 3 is directly or indirectlyconnected to the load that is to be handled.

The sliding motion backwards and forwards of the carriage 3 is effectedwhen the latter is actuated by a threaded screw 4, which may be rotatedin both directions by a drive motor, not shown, and which is made fromsteel or some other suitable material, and which preferably isconfigured as a high-efficiency ball screw. The ball screw 4 is formedwith threads 5 and in the conventional manner it is is drivinglyconnected with the carriage 3 via a ball nut 6.

Usually, e.g. depending on its length, the screw 4 extends freelythrough a through-bore 7 formed in one, as shown in FIG. 1, or two screwsupports 8 located one on either side of the carriage 3. For e.g. weightconsiderations, the screw supports 8 suitably are made from alight-weight material, preferably from extruded aluminium, plastics orthe like.

A driver means, designated by reference 9 and to be described in moredetail in the following, in turn displaces the screw supports 8backwards and forwards along the profiled rail 2 between end stoppositions spaced along the screw 4, and as mentioned earlier, the screwsupports serve to form bearings supporting the screw 4 intermediate endbearings 10 supporting the screw at the free ends of the latter.

In order to self-center the screw 4 in each individual screw support 8when the screw is rotating and when the screw supports assume theirrespective end stop positions, a self-centering element, generallydesignated by 11, is located in the through-bore 7 of each screwsupport. Each self-centering element 11 suitably is configured as atleast one slide member 12 arranged to slide across the outer peripheralsurface 13 of the screw 4. More precisely, the slide member or eachslide member 12 extends essentially in the longitudinal direction of thescrew 4 and is biased in a resilient manner and in an essentially radialdirection towards the screw into sliding abutment against the outerperipheral surface 13 of the screw 4. The resilient bias preferably iseffected by means of springs 15 mounted in holes 14 formed in each screwsupport 7, said springs 15 exerting pressure on the external or rearface 16 of each slide member 12.

As to the slide members 12, each such member may be designed in manyvarious ways, and FIGS. 1–6 and FIGS. 7 and 8 show respectively a firsta and second presently preferred embodiment.

The slide member 12 shown in FIGS. 1–6 is designed as an elongate plate17 extending essentially in the lengthwise direction of the screw 4, seeFIG. 5. The plate 17 is biased by two helical compression springs 15,which are placed in spaced-apart locations in the longitudinal directionof the screw, as is also apparent from FIG. 5. Preferably, the plate 17is manufactured from a comparatively hard material, such as a hardplastics material possessing extremely good sliding and wear-resistantproperties. For reception of the helical compression springs 15, theplate 17 is likewise formed with blind holes 18, and on its inner sideor front facing the screw 4 the plate 17 is essentially smooth toenhance its sliding and self-centering abutment against the outerperiphery 13 of the screw 4.

In order to ensure optimally even and efficient self-centering effectwhen the screw 4 rotates in either one of the rotational directionsthereof and when the screw supports 8 assume one of their end stoppositions, the slide members 12, designed as plates 17, preferably arespaced as evenly as possible around the screw 4. In the shownembodiment, three such plates 17 are spaced evenly around the screw.Alternatively, these plates could be arranged in one or several groupsabout the screw, an alternative that is not, however, shown herein. Thenumber of groups and of plates included in each group may be variedaccording to wish, for example depending on the size of the plates 17relative to the associated screw support 8, the size of the screwsupport itself, the diameter of the screw and so on.

In the embodiment of the slide member 12 shown in FIGS. 7 and 8, saidmember is designed as a sleeve 20 extending in the longitudinaldirection of the screw and in the shown embodiment it encloses the screw4 entirely and is disposed in the interstice or gap between thethrough-bore 7 of the associated screw support 8 and the outer periphery13 of the screw 4. Like the plate/plates 17 in the previous embodiment,the sleeves 20 are resiliently and essentially radially biased towardsthe screw 4. Suitably, this effect is obtained by means of helicalcompression springs 21 that correspond to the helical compressionsprings 15 and are spaced apart from one another in the longitudinaldirection of the screw and also spaced evenly about the screw 4, asappears from FIGS. 7 and 8. Like the plate/plates 17, the sleeve 20preferably is manufactured from a comparatively hard material, such ashard plastics, possessing extremely high sliding and wear-resistanceproperties. The helical compression springs 21 abut against the externalface 22 of the sleeve 20, and like the inner face of the plate/plates17, the inner face 23 of each spring facing the screw 4 is essentiallysmooth to enhance the sliding and self-centering abutment of the sleeveagainst the outer periphery 13 of the screw 4.

The sleeve 20 may be designed otherwise than as one integral sleevewholly enclosing the screw. For example, it could be composed of severalannular components positioned concentrically in succession in thelongitudinal direction of the screw, each one of them being biased inthe manner indicated above. Another alternative is to slit the sleeve inthe longitudinal direction of the sleeve and of the screw or toconstruct the sleeve from elongate arc segments arranged in abuttingrelationship along their long edges or with clearances between thesegments in the circumferential direction. Additional alternativesexist; the choice depends on the size of the sleeve 20 relative to theassociated screw support 8, the size of the screw support itself, thediameter of the screw and so on, as mentioned previously.

The previously mentioned driver means generally designated by reference9, serving to displace the screw supports 8 between the end stoppositions of the latter, is shown in FIGS. 1–3 and 9A, B, and C. Thedriver means 9 kinetically interconnects the two screw supports 8 oneither side of the carriage 3. More precisely, the interconnection issuch that when the carriage, while being displaced in a sliding motionin one direction by means of the ball screw 6, abuts against one of thescrew supports 8 located on one side of the carriage 3 and displacesthat screw support from one to the other of the end stop positions ofthe latter, it will also, via the driver means 9 bring along in itsmotion the other screw support 8 located on the opposite side of thecarriage 3. As the carriage is displaced in a sliding motion in theopposite direction, the procedure as described above is repeated but inthe reverse order.

Thus the driver means 9 is fixedly connected with the screw supports 8and extends freely past the carriage 3.

In accordance with the preferred embodiment illustrated in FIGS. 1–3 andFIGS. 9A, B, and C, the driver means 9 preferably is designed as a pullrod 24 suitably made from extruded aluminium or steel. At its free ends25 the pull rod 24 is attached in any known manner to the associatedscrew support 8, its ends being guided in the profiled rail 2 of thelinear unit 1 beyond and spaced from the carriage 3. More precisely, thepull rod 24 is guided with a suitable sliding fit in an elongate guidemeans 27 formed in the profiled rail 2. An elongate guide portion 28 ofthe pull rod 24, located inside the guide means, and the guide means 27itself are configured with essentially complementary profile shapes,preferably a circular shape.

In the shown embodiment, the free attachment ends 25 of the pull rod 24form an angle, e.g. of essentially 90°, to the guide portion 28 of saidrod. Intermediate each attachment end 25 and the guide portion 28, thepull rod is formed with a transitional portion 29 passing through anelongate recess 30 that is formed in the guide means 27 and that is opentowards the screw supports 8, see FIG. 2. To ensure that the guidingfunction of the pull-rod guide portion 28 in the guide means 27 is notjeopardised, the transitional portion 29 and the recess 30 are givenless substantial, that is smaller dimensions than the guide portion 28and the guide means 27.

In accordance with one embodiment, not shown, two or several screwsupports 8, arranged in pairs, are provided on either side of thecarriage 3. In this case, the screw supports of the first pair closestto the carriage on either side thereof are kinetically interconnected bymeans of a first pull rod corresponding to pull rod 24, and the screwsupports of the pair or other pairs, located beyond the nearest pairs,are kinetically interconnected in pairs by means of one further pull rodeach, corresponding to pull rod 24 but longer than the latter. Owing tothis construction, displacement of one of the screw supports of thefirst pair in response to actuation thereon by the carriage 3, as thelatter is sliding in one direction along the screw 4, will result inabutment of that screw support against the closest screw support of thenext pair for displacement of said support, and so on, depending on thenumber of screw-support pairs, and reversely as the carriage 3 isdisplaced in a sliding motion in the opposite direction.

As will be appreciated, the invention should not be regarded asrestricted to the embodiments shown and described herein but could bemodified in various ways within the scope of the protection defined inthe appended claims.

1. A device for linear drive units comprising: a profiled rail alongwhich a carriage is arranged for sliding movement backwards and forwardsin response to actuation from a threaded screw, said screw arranged torotate in opposite directions and being drivingly connected with thecarriage and, on either side of the carriage, passing through athrough-bore in at least two screw supports, said screw supports beingarranged to be displaced by a driver means for movement backwards andforwards along the profiled rail between two end stop positions andforming bearing means carrying said screw intermediate at least two endbearings that support the screw at the ends of the said screw, whereinthe driver means kinetically interconnects the screw supports located oneither side of the carriage, and wherein the carriage, when beingslidingly displaced in one direction, abuts against the screw support onone side of the carriage for displacement of that screw support from oneof the end stop positions, said carriage simultaneously, by means of thedriver means bringing, along in its movement of the screw supportlocated on the other side of the carriage, and reversely.
 2. The deviceas claimed in claim 1, wherein the driver means is fixedly attached tothe screw supports and extends freely past the carriage.
 3. The deviceas claimed in claim 1, wherein the driver means is a pull rod havingfree ends of which are attached to the associated screw support andwhich pull rod intermediate its attachment ends are guided in theprofiled rail of the linear unit beyond and spaced from the carriage. 4.The device as claimed in claim 3, wherein the pull rod is fitted into anelongate guide means in the profiled rail of the linear unit to beguided therein, a guide portion of the rod that is located in the guidemeans and the guide means being configured with essentiallycomplementary profile shapes.
 5. The device as claimed in claim 4,wherein the free attachment ends of the pull rod form an angle to theguide portion of the rod and wherein intermediate each one of itsattachment ends and the guide portion, said pull rod is formed with atransitional portion passing through an elongate recess that is formedin the guide means and is open towards the screw supports.
 6. The deviceas claimed in claim 5, wherein said transitional portion and the recesshave smaller dimensions than the guide portion and the guide means. 7.The device as claimed in claim 1, wherein there are at least two screwsupports pairs arranged in pairs on either side of the carriage, andwherein the screw supports of a first pair closest to the carriage oneither side thereof are kinetically interconnected by means of a firstpull rod and a screw support of at least one second pairs located beyondthe first at least one pairs, are kinetically interconnected in pairs bymeans of one further pull rod each, whereby displacement of one of thescrew supports of the first pair in response to actuation thereon by thecarriage, will result in abutment of that screw support against theclosest screw support of said second pair for displacement of both ofsaid supports and their respective pair, and reversely as the carriageis displaced in a sliding motion in the opposite direction.
 8. Thedevice as claimed in claim 1, wherein a self-centering element locatedin the through-bore of the screw support is provided, which element hassliding abutment contact with the screw both when the screw is rotatingin one or the other of its directions and when the screw supports assumetheir end stop positions, in order to self-center the screw in the screwsupport.
 9. The device as claimed in claim 8, wherein the self-centeringelement is configured as a slide member that slides on top of the outerperiphery of the screw.
 10. The device as claimed in claim 9, whereinthe slide member is formed by a plate, which extends essentially in thelengthwise direction of the screw and which is resiliently biased in anessentially radial direction towards the screw.
 11. The device asclaimed in claim 8, wherein several slide members are provided, saidmembers being evenly spaced and/or arranged in one or several groupsaround the screw.
 12. The device as claimed in claim 9, wherein theslide member is formed by a sleeve, said sleeve extending in thelongitudinal direction of the screw and enclosing said screw and beingresiliently biased in an essentially radial direction towards the screw.13. The device as claimed in claim 12, wherein the sleeve is positionedin a gap between the through-bore of the screw support and the outerperiphery of the screw.
 14. The device as claimed in claim 13, whereinat its inner face, the sleeve slidingly abuts against the outerperiphery of the screw whereas at its outer face said screw isresiliently biased in an essentially radial direction towards the screwby means of at least one spring means directed in an essentially radialdirection towards the screw.
 15. A device for linear-drive unitscomprising: a profiled rail along which a carriage is arranged forsliding movement backwards and forwards in response to actuation from athreaded screw, said screw arranged to rotate in opposite directions andbeing drivingly connected with the carriage and, on the other side ofthe carriage, passing through a through-bore, in at least two screwsupports, said screw supports being arranged to be displaced by a pullrod for movement backwards and forwards along the profiled rail betweentwo end stop positions and forming bearing means carrying said screwintermediate at least two end bearings that support the screw at theends of the said screw, wherein the pull rod kinetically interconnectsthe screw supports located on either side of the carriage and whereinthe carriage, when being slidingly displaced in one direction, will abutagainst the screw supports on one side of the carriage for displacementof that screw support from one of the end stop positions of the saidscrew to the other end stop position, said carriage simultaneously bythe pull rod brings along its movement of the screw support located onthe other side of the carriage, and reversely.
 16. The device as claimedin claim 15, wherein the pull rod is fixedly attached to the screwsupports and extends freely past the carriage.
 17. The device as claimedin claim 15, wherein the pull rod has free ends which are attached tothe associated screw supports and the free ends are guided in theprofiled rail spaced from the carriage.